Field of the Invention
This invention concerns a phosphor bronze alloy excellent in migration resistance.
Description of the Prior Art
With the increasing demand for reducing the thickness and decreasing the size of electric and electronic components in recent years the number of electrodes has tended to be increased, for example, in integrated circuits and resistors. Along with the increase in the number of electrodes, pitches between electrodes are reduced from 1/10 inch to 1/20 inch and further to 1/30 inch due to the requirement of mounting them to printed circuit boards at a high density and in a reduced thickness and, correspondingly, the inter-electrode pitch of terminals and connectors are also decreased quite in the same manner. However, if the inter-electrode pitch in the electric or electronic components is reduced, water is deposited between the electrodes due to the condensation of moistures or intrusion of water. Copper ions are leached out at the portion deposited with water, the copper ions thus leached out are reduced by the electric potential between the electrodes and the thus reduced copper ions are deposited as metal copper. Such leaching, reduction and deposition occur repeatedly and, as a result, crystals of the deposited copper metal grow from the cathode and reach as far as the anode. Such a phenomenon is generally referred to as migration. If such migration occurs, short-circuit is resulted between the cathode and the anode.
The migration is liable to occur in phosphor bronze. Although it has been known that migration less occur in brass, brass has a defect of possibly suffering from stress corrosion crackings.